1. Field of the Invention
This invention relates generally to apparatus for boring an opening in the side wall of a hollow member, and more particularly to apparatus for boring a sewer pipe opening in the side wall of a manhole base.
2. Description of the Prior Art
Manholes are commonly provided in sanitary and storm sewer lines, and commonly comprise a cylindrical concrete base section having an integral bottom and an open upper end; the base section is in essence a section of bell and spigot concrete pipe with the spigot end facing upwardly and a poured bottom wall at what otherwise would be the bell end. Depending upon the depth of the manhole, other sections of bell and spigot concrete pipe may be placed on top of the base section.
It is necessary to provide openings in the side wall of the base section of a manhole, or sometimes in upper sections, to receive sewer pipe. The sewer pipe connections to the manhole are not necessarily at diametrically opposite points, i.e., they may be radially and/or vertically displaced with the result that the sewer pipe openings in each manhole must be customed-positioned depending upon the location of the manhole in the sewer system.
In the past, sewer pipe openings in manhole sections have been customed-located when the manhole section was initially cast by the use of a suitable mandrel or mandrels. However, it is not uncommon for the location of a given sewer line to deviate from the plan and thus, the location of the sewer pipe openings in a particular custom-cast manhole may not be correct when the manhole section is delivered to the site, which has resulted in scrapping the section.
Apparatus has been provided for boring sewer pipe openings in the side wall of a manhole section from the outside; however, it has been difficult to secure the apparatus to the manhole section with the result that the diamond tips on the boring bits tend to tear-off thus destroying the bit.
It is therefore desirable to provide an improved apparatus for boring openings in the side wall of a hollow member, such as a concrete manhole section, in which the boring apparatus is securely located with respect to the hollow member.